1. Field of the Invention
The present invention generally relates to a method of and apparatus for reproducing in formation recorded on a called CLV (Constant Linear Velocity) type record medium such as a CD (Compact Disk)--ROM (Read Only Memory) of CLV
2. Description of the Related Art
The CD for music is well known as an record medium which has a memory capacity of large volume. Thus, there has been developed a CD-ROM, which is a CD recorded with the computer readable data such as program and data base instead of music signals. The CD-ROM is advantageous it is suitable for the mass production so that the production cost is relatively low. Thus, the CD-ROM has been a very popular record medium f or the recent
Since the CD-ROM is recorded with the data for computer or the compressed digital video signals etc. instead of the music signals, from the view point of keeping the high recording density, the CD-ROM is basically recorded as a CLV type record medium, i.e. recorded by the constant linear velocity, in the same manner as the CD f or music.
In case what the CD-ROM of CLV type is used as an external ROM for the computer, it is preferable to decrease the access time i.e. the time required for the optical pickup to move to a specific position where the desired data are recorded on the optical disc. However, in case of the CD-ROM of CLV type, in order to keep the linear velocity constant during the rotation of the optical disc, it is necessary to change the rotation angular velocity in accordance with the radial position on the optical disk. Namely, the rotation angular velocity for reading a position near the inner circumference on the optical disc should be much lower than that near the outer circumference on the optical disc. Here, since the change in the rotation angular velocity requires a certain period of time, the CD disc of CLV type has an essential disadvantage to decrease the access time when the CLV type reproducing operation is performed.
Therefore, there may be proposed to reproduce the CD disc of CLV type by the CAV (Constant Angular Velocity) type reproducing operation. However, since data on the CD disc of CLV type are recorded on the assumption that they will be reproduced under the condition that the linear velocity is constant (i.e. by the CLV reproducing operation), if the CD disc of CLV-type would be reproduced under the condition that the angular velocity is constant (i.e. by the CAV reproducing operation), the transmission rate of the data is greatly changed between the reproduction near the outer circumference of the disc and the reproduction near the inner circumference of the disc.
More concretely, assuming that the number of rotation of the disc is about 1000 r.p.m. (rotation per minute), the data transmission rate is about 350 kBytes/sec at the most inner circumference on the disc while it is about 875 kBytes/sec at the most outer circumference on the disc. Namely, the difference in the transmission rate therebetween is as much as about 2.5 times.
In this case, the signal process unit in the CD player, which processes the data read out from the CLV type disc, should have the process capability of processing the data transmitted by the highest transmission rate (i.e. about 875 kBytes/sec).
However, when the data are read out from the portions other than the most outer circumference on the disc, since the data are only read out by the transmission rate lower than the data process rate of the process unit, an effective signal process cannot be performed by the signal process unit, which is a serious problem in a practical sense.